law enforcement in washington in new york, in san francisco, are in a heightened state of alert. and miami dade police officials say they have increase d the event that attracts half a million spectators each year. today was a very sad day for athletics and for our friends in marathon running. our security plan is developed jointly with the metropolitan police and we were in contact with them soobs we heard the news. >> why don't we get back to the scene. you have new information for us? >> don, we do know now that officials are going to brief reporters at 9:30 just a few hours away. there is so much we don't know. we do not know if this attack was a foreign or domestic attack. but right now investigators are behind me on exitor street. they have set up about six or seven blocks. they are setting up barriers to make the security tighter, don. we're still waiting to hear very much tonight. >> one of the big clues will be the two devices which were not detonated. what sort of clues and information are the authorities expecting to get from that? >> we heard bob earlier talking about